Solution-Printed Organic Semiconductor Blends Exhibiting Transport Properties on Par with Single Crystals

Solution-printed organic semiconductors have emerged in recent years as promising contenders for roll-to-roll manufacturing of electronic and optoelectronic circuits. The stringent performance requirements for organic thin-film transistors (OTFTs) in terms of carrier mobility, switching speed, turn-on voltage and uniformity over large areas require performance currently achieved by organic single-crystal devices, but these suffer from scale-up challenges. Here we present a new method based on blade coating of a blend of conjugated small molecules and amorphous insulating polymers to produce OTFTs with consistently excellent performance characteristics (carrier mobility as high as 6.7 cm2V−1s−1, low threshold voltages of \u3c1V and low sub threshold swings \u3c0.5Vdec−1). Our findings demonstrate that careful control over phase separation and crystallization can yield solution-printed polycrystalline organic semiconductor films with transport properties and other figures of merit on par with their single-crystal counterparts

Review of the Common Deposition Methods of Thin-Film Pentacene, Its Derivatives, and Their Performance

Pentacene is a well-known conjugated organic molecule with high mobility and a sensitive photo response. It is widely used in electronic devices, such as in organic thin-film transistors (OTFTs), organic light-emitting diodes (OLEDs), photodetectors, and smart sensors. With the development of flexible and wearable electronics, the deposition of good-quality pentacene films in large-scale organic electronics at the industrial level has drawn more research attention. Several methods are used to deposit pentacene thin films. The thermal evaporation technique is the most frequently used method for depositing thin films, as it has low contamination rates and a well-controlled deposition rate. Solution-processable methods such as spin coating, dip coating, and inkjet printing have also been widely studied because they enable large-scale deposition and low-cost fabrication of devices. This review summarizes the deposition principles and control parameters of each deposition method for pentacene and its derivatives. Each method is discussed in terms of experimentation and theory. Based on film quality and device performance, the review also provides a comparison of each method to provide recommendations for specific device applications

Orthogonal printing of uniform nanocomposite monolayer and oriented organic semiconductor crystals for high-performance nano-crystal floating gate memory

Inkjet printing is of great interest in the preparation of optoelectronic and microelectronic devices due to its low cost, low process temperature, versatile material compatibility, and ability to precisely manufacture multi-layer devices on demand. However, interlayer solvent erosion is a typical problem that limits the printing of organic semiconductor devices with multi-layer structures. In this study, we proposed a solution to address this erosion problem by designing polystyrene-block-poly(4-vinyl pyridine)-grafted Au nanoparticles (Au@PS-b-P4VP NPs). With a colloidal ink containing the Au@PS-b-P4VP NPs, we obtained a uniform monolayer of Au nano-crystal floating gates (NCFGs) embedded in the PS-b-P4VP tunneling dielectric (TD) layer using direct-ink-writing (DIW). Significantly, PS-b-P4VP has high erosion resistance against the semiconductor ink solvent, which enables multi-layer printing. An active layer of semiconductor crystals with high crystallinity and well-orientation was obtained by DIW. Moreover, we developed a strategy to improve the quality of the TD/semiconductor interface by introducing a polystyrene intermediate layer. We show that the NCFG memory devices exhibit a low threshold voltage (100 cycles), and long-term retention (>10 years). This study provides universal guidance for printing functional coatings and multi-layer devices

Flexible Ultralow-Power Sensor Interfaces for E-Skin

Thin-film electronics has hugely benefitted from low-cost processes, large-area processability, and multi-functionality. This has not only stimulated innovation in display and sensor technology, but has also demonstrated great potential for integration of components for human-machine interfaces. For electronics to be deployed as sensor interfaces and signal processing, the quest for low power is compelling due to the inherently limited battery lifetime. This review will present the state-of-the-art in thin film electronics and demonstrate examples of low-cost printable transistors and biosensors that are flexible/stretchable for wearable and other applications. Ultralow power design for thin-film transistors will be discussed from the standpoint of reducing both operating voltage and operating current, taking into account the challenges in meeting frequency requirements. Compact models for circuit design will be reviewed along with new insights into ultralow power transistors and high gain amplifier circuits. Finally, a concept for an integrated system comprising sensors and interfacing circuits will be demonstrated, which has the potential to enable battery-less operation.EPSRC under Project EP/M013650/1 EU under Projects DOMINO 645760, 1D-NEON 685758 and BET-EU 692373 IEEE Electron Devices Society PhD Student Fellowship China Scholarship Counci

Next-generation organic blend semiconductors for high performance solution-processable field Effect Transistors

Ambitions for transparent, lightweight, flexible and inexpensive electronic technologies that can be printed over large area substrates have driven substantial advances in the field of organic/printed electronics in recent years. Amongst the various technologies investigated, solution-processed, organic thin-film transistors (OTFTs) have received extraordinary attention, primarily due to the enormous potential for simple, cost-effective manufacturing. Two exciting research areas relevant to OTFT development that offer tremendous potential are those of the small molecule/polymer organic semiconducting blends and the science and engineering of molecular doping. However, the lack of organic semiconducting blends that surpass the benchmark charge carrier mobility of 10 cm2/Vs, and the numerous challenges associated with the practical utilisation of molecular doping, have prevented adaptation of OTFTs as a viable technology for application in the emerging sector of plastic electronics. The work in this thesis focuses on an organic semiconducting system for OTFTs that addresses these two points. The first part of this thesis describes the development of advanced organic semiconducting blends, the so-called 3rd generation (3G) blend systems. Specifically, a new blend based on the small-molecule C8-BTBT and the conjugated polymer C16DT-BT is introduced. A third component, the molecular p-dopant, C60F48, is then added to the blend system and it is found to have remarkably positive effects on OTFT performance. The ternary blend system is then combined with a solvent-mixing approach, resulting in devices with an exceptional hole mobility value exceeding 13 cm2/Vs. Through the use of complementary characterisation techniques, it is shown that key to this achievement is the unusual three-component material distribution, hinting at the existence of an unconventional doping mechanism. Furthermore, by considering alternative processing techniques, the maximum mobility of the resulting OTFTs is improved further to a value in excess of 23 cm2/Vs. The second part of the thesis focuses on the impact of p-doping in the ternary C8 BTBT:C16IDT BT:C60F48 blend on other important operating characteristics of the OTFTs. The intentional and simple to implement doping process is shown to improve key device parameters such as bias-stress stability, parasitic contact resistance, threshold voltage and the overall device-to-device parameter variation (i.e. narrowing of the parameter spread). Importantly, the inclusion of the dopant is not found to adversely affect the nature of the C8 BTBT crystal packing at the OTFT channel. The final part of this thesis describes the incorporation of 3G blend-based OTFTs into fully functional logic electronic circuits. Hybrid inverter circuits (i.e. NOT gates) are fabricated at low temperatures from solution-phase by combining the high hole mobility C8-BTBT:C16IDT-BT:C60F48 blend OTFTs as the p-channel device and a novel In2O3/ZnO heterojunction metal oxide semiconducting system as the n-channel transistor. The resulting complementary inverters exhibit excellent signal gain and high noise margins, making this hybrid circuitry a promising contender for application in the emerging field of printed microelectronics.Open Acces

A review on materials and technologies for organic large-area electronics

New and innovative applications in the field of electronics are rapidly emerging. Such applications often require flexible or stretchable substrates, lightweight and transparent materials, and design freedom. This paper offers a complete overview concerning flexible electronics manufacturing, focusing on the materials and technologies that have been recently developed. This combination of materials and technologies aims to fuel a fast, economical, and environmentally sustainable transition from the conventional to the novel and highly customizable electronics. Organic conductors, semiconductors, and dielectrics have recently gathered lots of attention since they are compatible with printing technologies, and can be easily spread over large and flexible substrates. These printing technologies are usually simple and fast procedures, which rely on low-cost and recycle-friendly materials, intended for large-scale fabrication. Overall, even though organic large-area electronics manufacturing is still in its early stages of development, it is a field with tremendous potential that holds promise to revolutionize the way products are designed, developed, and processed from the factory premises to the consumers’ hands. Besides, this technology is highly versatile and can be applied to a large array of sectors such as automotive, medical, home design, industrial, agricultural, among others.This work was supported by NORTE-06-3559-FSE-000018, integrated in the invitation NORTE-59-2018-41, aiming the Hiring of Highly Qualified Human Resources, co-financed by the Regional Operational Programme of the North 2020, thematic area of Competitiveness and Employment, through the European Social Fund (ESF), and by the scope of projects with references UIDB/05256/2020 and UIDP/05256/2020, financed by FCT – Fundação para a Ciência e Tecnologia, Portugal. The authors also thank Prof. Luís A. Rocha for his support and guidance during the writing of this review work

INCREASING ORGANIC SEMICONDUCTOR PERFORMANCE THROUGH CHEMICAL AND PROCESSING MODIFICATIONS

This thesis focuses on tuning molecular packing of organic semiconductors through processing or chemical modifications to increase performance and establish structure-property relationships. Chapter 2 utilizes differing processing techniques to alter the molecular packing of bistetracene in the thin film and thorough polymorph characterization to relate the modification of molecular packing to the increase in charge mobility and mechanism. Chapter 3 introduces the oligomer as a model system to resolve issues that would be difficult or impossible using polymeric systems, due to their monodispersity and increased crystallinity allows for more detailed structural characterization. In this chapter we determine a crystal packing and melting point alternation in BTTT monomers, a trend well documented within organic small molecules, yet largely ignored within the organic semiconductor community. A series of BTTT dimers with various side chains lengths were synthesized in Chapter 4 to quantify the effect of side chain length on bimolecular crystal formation with PCBM using smaller side chains, outside the solubility limit of the parent polymer, and discovered and characterized a phase transition from a bimolecular crystal to amorphous blend upon decreasing side chain length, greatly influencing the electronic properties of the blends. Chapter 5 expands on the knowledge of the previous chapter, designing BTTT dimers with variable side chains using side chains that fall on both sides of the phase transition to investigate the influence of side chain position and size on molecular packing and blended morphology. In Chapter 6, using the benchmark BTTT dimer, we explore the effect of dopant chemical structure on morphology and conductivity of blended films. Surprisingly, the doping mechanism differs from that of the parent polymer, and by tuning the dimer/dopant interactions, demonstrate a differing morphology and large variation in conductivity dependent on dopant choice